Let's get rid of the big myth about Hoover Dam right now. There are no bodies buried in the concrete of this colossal structure that holds back the Colorado River. Completed 70 years ago this month, the dam does, however, feature a number of plaques and a monument near its visitor's center that honor the men who built it - including the 110 workers who died in the process.
Straddling the state border of Arizona and Nevada, this water conservation and hydroelectric power plant is one of the outstanding engineering accomplishments of the 20th century. It rises more than 726 feet from bedrock, is 660 feet thick at the base, 45 feet wide at top, and its crest stretches 1,244 feet across the canyon. More than five miles of maintenance and inspection tunnels are built into the structure. (Many are lined with ceramic tile and American Indian art designs.)
Black Canyon was selected as the best site for the dam because it was narrow and had high, strong, sheer walls. With the Great Depression sweeping the country, finding men eager to do the backbreaking and often-dangerous work was no problem. Work officially began in May 1931.
By 1933, the concrete began to be poured - and it would flow day and night for two years. When it was finished, more than 3.25 million cubic yards of hard concrete were in place.
Bid at just under $49 million - the largest construction contract led by the federal government up to that time - Hoover Dam was completed in four and a half years - two and a half years ahead of schedule. (Imagine that happening today!) The overall cost of the project, including the dam, power plants and related structures, was $165 million.
The multipurpose dam was built to harness the Colorado River for flood control, navigation, irrigation, water storage and power. In the bargain, the project was to be self-supporting, financed entirely through the sale of the hydroelectric power generated
Just 30 miles south of Las Vegas, Hoover Dam is the third most popular tourist attraction in the United States under the control of the federal government. The two-lane road from Las Vegas to the dam snakes through a desert landscape that hasn't changed in thousands of years.
Visiting motorists will crest a knoll and then face a huge oasis - Lake Mead, a man-made body of water that extends more than 110 miles upstream from the dam.
Tourists can learn about the dam, its history and construction, when they visit a visitor's center built into the Nevada side of the canyon wall. The center has a rooftop overlook and, for a fee, visitors can take a tour that departs from the center.
Many visitors walk across the dam from one state to the other, and the roadway atop the dam is highly traveled Highway 93. Traffic moves across slowly, and the sidewalk is comfortably wide.
However, walking along the top of the structure and peering over the edge of the face of the dam is a stomach-churning experience. A number of small platforms hang out over the top of this concrete monster, allowing views down the sloping face.
The front of the dam sweeps down and away. The back, water side of the dam presents a much more serene scene.
Memorial art and sculptures are displayed atop the dam, including a 142-foot-high flagpole flanked by two winged figures. Other art deco works include a large compass surrounded by the 12 signs of the zodiac. Visitors gazing upon these works will be walking on an intricate terrazzo floor displaying a star map.
Did you know …?
Hoover Dam was originally named in honor of Herbert Hoover's contributions to the project when he served as U.S. Secretary of Commerce in the 1920s. When President Roosevelt took office, his secretary of the interior changed the name to Boulder Dam. President Truman changed it back to Hoover Dam permanently, via an Act of Congress in 1947.
When construction of the Hoover Dam began, diversion tunnels were drilled and blasted through solid rock in the walls along either side of the Colorado River. These massive tunnels were 4,000 feet long, 56 feet in diameter, and surrounded by 3 feet of concrete.
Then, a structure was built to divert the river into the tunnels. Another structure was built downstream to keep water from backing up into the proposed dam site, where the riverbed was excavated 135 feet to bedrock.
Cooling the concrete was a major technical challenge facing the engineers, and they resolved it with an innovative idea. Without artificial cooling, it would have taken more than a century for the dam to lose the heat created by the setting concrete; and it would have shrunk and cracked as it cooled. The solution, engineers determined, was to build the dam in pier-like blocks and cool the concrete by running ice-cold water through a network of copper pipes embedded in the blocks. As the blocks contracted and gaps appeared between them, concrete grout was pumped into the breaches, making the structure monolithic. The copper tubes were filled with concrete as the material cured, assuring structural integrity.
Water has never crested the dam. Instead, it runs around the dam, and detailed engineering diverts the flow to the power-producing generators at the base of both canyon walls. The power plants at Hoover Dam have 17 large generators with a capacity of more than 1.3 million kilowatts.
Two spillways on either side are 27 feet lower than the walk and roadway atop the dam.
Back in 1941, the lake was permitted to rise so that the spillways could be tested. Mother Nature provided another successful test of the spillways when snowmelt reached record highs in 1983. A white line along the canyon walls behind the dam shows the maximum level reached.
Where does all that energy go?
With the border between Arizona and Nevada running down the middle of the Colorado River, each state has a set of turbines inside the base of the Hoover Dam. The water passing through these turbines generates low-cost hydroelectric power for use in Nevada, Arizona and California. The energy is marketed to both public and private agencies under contracts that expire in 2017. The four biggest users are the Metropolitan Water District of Southern California, Nevada, Arizona and Los Angeles.
During World War II, the dam and the surrounding area were closed off, and the site was guarded around the clock. Security remained in place until after the war, and the dam reopened to the public on Sept. 2, 1945.
Checkpoints have been installed on the roads approaching the dam since Sept. 11. Tours are no longer given within the dam. However, a visitor's center tour takes tourists into the wall of Black Canyon, where they can view the Nevada wing of the power plant and its generators.
In the works …
In a couple of years, motorists can avoid the tourists by using the Hoover Dam Bypass. It will be a four-lane, three and a half mile divided highway flanking an innovative arch bridge that spans the Black Canyon. It will route traffic away from the top of the dam, relieving bottlenecks, and adding greater security.
The project is scheduled for completion in 2008.
To learn more …
To find out more about the dam, visit the dam's official Web site: http://www.usbr.gov/lc/hooverdam/
At the site, visitors can find up-to-date information about parking and tour costs, operating hours, and driving instructions.
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